You can set up ES to use external stopword list file(s) so you can add/remove words as you see fit with your data. Certainly I suggest you to start with the default list comes from ES until you see something that does not seem to work with your data, then try the custom list using external file.
Here is the link where you can get a decent set of stopword lists for different languages to start with: http://www.ranks.nl/stopwords